The goals of this project are 1) to produce antibodies against defined regions of the major histocompatibility complex; 2) to characterize the reactions of these antibodies with the cell surface of lymphocytes and to determine the nature of the cells bearing individual antigens; and 3) to attempt to produce anti-idiotypic antibodies against the receptors on these antibodies which detect cell surface histocompatibility antigens. The relationship between Ia antigens and the Fc receptor will be pursued. Other non-H-2 antigens also associated with the Fc receptor will be investigated, as will the Fc receptor of other cell populations such as macrophages and T cells.